1. Field of the Invention
The present invention relates to a process for removal of impurities from phenol by means of at least one acid catalyst.
2. Description of the Background
The synthesis of phenol by decomposition of cumene hydroperoxide is known. The reaction mixture obtained during decomposition is generally subjected to fractional distillation after it has been neutralized. During this distillation acetone is removed by distillation as the first main product. Thereafter, as the distillation is continued, the remaining isopropylbenzene, xcex1-methylstyrene and water are also obtained in other fractions. Thereafter, crude phenol is removed by distillation in an overhead as the second main product, while a mixture of phenol, acetophenone, dimethylphenylcarbinol and p-cumylphenol together with numerous condensation and polymerization products remain in the bottoms of the distillation column. This crude phenol still contains impurities, which makes difficult or severely interferes with further processing of the phenol to derivative products. These impurities are, in particular, ketones, such as mesityl oxide, isomesityl oxide, methyl isobutyl ketone, hydroxyacetone and acetophenone, unsaturated compounds and/or methylbenzofuran. These compounds cannot be completely removed from the phenol by distillation.
German Patent No. 1668952 describes a process for preparing pure phenols which are almost free of mesityl oxide from crude phenols which form during decomposition of hydroperoxides of alkylaromatic hydrocarbons in the presence of acids followed by fractionation of the reaction mixture, by passage over stationary-bed catalysts of macroreticular ion exchangers containing active sulfonic acid groups or similar active acid groups at temperatures ranging from 45 to 200xc2x0 C. and subsequent distillation. In this process the treatment of the crude phenols in liquid or vapor phase is accomplished without admixture of water. If necessary the reaction mixture is neutralized before distillation is performed. By means of this process weakly reactive carbonyl compounds such as methyl isobutyl ketone and methylcyclopentenone, as well as compounds such as 2-methylbenzofuran cannot be removed from the crude phenol at all, or can only be removed incompletely. The presumed reason for this is that equilibrium is established between the substances being withdrawn and the reaction products, and that further reaction of the reaction products is prevented by water formed during the reaction.
U.S. Pat. No. 5,414,154 teaches a process for reducing methylbenzofuran impurities in phenol obtained from the decomposition of cumene hydroperoxide. In this process the crude phenol is treated in such a way that it has an acetol content of less than 260 ppm. The crude phenol treated in this manner is contacted with an acid catalyst, whereby methylbenzofuran is converted to higher-boiling compounds, which are removed from the crude phenol by distillation. Implementation of this process is limited to the use of crude phenol having an acetol content of less than 260 ppm. A need continues to exist for removing impurities from phenol produced by the decomposition of cumene hydroperoxide.
Accordingly, one object of the present invention is to provide a process for the removal of impurities from phenol, which process, largely regardless of the composition of the impurities, is capable of separating phenol from impurities in a manner which is simple and uses the least possible amount of energy.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a process of removing impurities from phenol comprising: first treating phenols containing impurities with at least one acid catalyst which converts the impurities into compounds which can be separated from phenol, separating the acid treated phenol from said compounds; and treating the separated phenol a second time with at least one acid catalyst, thereby effectively removing reactive impurities from phenol. The composition of the impurities has very little influence on the efficiency of the process.
Another aspect of the invention is a process of synthesizing phenol by removing impurities therefrom by the procedure set forth above.